1. Field of the Invention
The invention relates in general to machines for automated processing of mailpieces, and in particular to a dynamic speed control system for improving throughput rate in an insertion machine.
2. Related Art
Computer-controlled insertion machines have been known for providing high-speed, automated insertion of documents into envelopes. Such insertion machines typically include a continuous form feeder, or "roll unwind," for supplying a web of attached sheets (or a sheet feeder for supplying individual sheets), with several adjacent sheets being associated together as a set; a burster or cutter for separating the web into individual sheets, those sheets including for each set a master document having an optical mark thereon for providing insertion instructions and other information about the set; a reader for reading the optical mark and providing the information therein to a central computer; an accumulator for accumulating individual sheets fed seriatim thereto into stacked sets; a folder for folding the sets; a series of insert hoppers for selectively feeding inserts onto the folded sets as the sets travel past the hoppers on an insert track/conveyor; an insert station for inserting each set and its associated inserts into an envelope; a sealer for sealing and closing the flap on the envelopes; and, a postage meter for applying postage to the completed mail piece.
The "base inserter" (also referred-to herein as the "base machine" or "host inserter") of the above-described machines, e.g., the insert hoppers and all devices downstream from them, can typically operate at a constant, high throughput rate. To take full advantage of that throughput rate, however, sets must be accumulated by upstream devices of the machine (e.g., the burster, reader, accumulator and folder) and delivered to the base inserter at a rate which equals the base inserter's constant throughput rate.
If all sets are identical, e.g., if all sets have the same number of sheets (referred to herein as "set size") and all sheets have the same form length, then each of the upstream devices can be set to output its product at a rate which is tied to the base inserter's throughput rate and the throughput of the entire machine can be maximized. For example, if the base inserter is operating at a throughput of 100 inches-per-second (ips), and two-sheet sets are being accumulated, then the accumulator can output sets at 100 ips and the burster and reader can output single sheets at 200 ips.
However, if individual sets in a batch vary in set size and/or form length, then if the above relationships between output speeds remain constant, the rate at which sets are delivered to the base inserter will vary as the set size or form length varies. Because this delivery rate varies, it cannot be set so as to be constantly optimized for a constant rate at which the base inserter is operating.
Individual devices in typical machines of the prior art have been programmed to process and feed out documents or sets of documents "on-demand." That is, when a device finishes processing a particular document or set of documents, it waits to output its document(s) until it receives a message from the next downstream device stating that the downstream device is ready to receive the document(s). Thus, a bottleneck at a particular device can cause all upstream devices to be slowed, resulting in a reduced total throughput of the machine.
Further, in typical computerized insertion machines of the prior art, each device is operated synchronously. That is, each device outputs its documents in synch with a machine cycle. If the next downstream device is not ready to receive those documents at a particular machine cycle, the device holds its contents until the next machine cycle. However, this results in further reduction of throughput in that there may be a time lag between the time at which the downstream device is ready and the next machine cycle.